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«—【Preamble】】 —»
"Hot search: Nearly half of China's cities are sinking! More coastal land may be below sea level in the future"
Could it be that in the near future, our cities will really be flooded by the sea?
Most cities in China are facing land subsidence
In fact, this conclusion comes from a study published in Science, which showed that most cities in China face land subsidence.
About 16% of these cities, such as Beijing, Tianjin, Harbin, Zhengzhou and other areas, have some land subsidence of more than 10 mm per year. In nearly half of cities such as Shanghai, Suzhou, Dalian, Shenyang and other regions, some ground subsidence exceeds 3 mm per year.
Hazards of land subsidence
10 millimeters of sedimentation per year may seem like a small number, but time can magnify the impact of all small things countless times.
If we don't do anything to allow the ground to sink, in 100 years, 22 to 26 percent of the continent's coastal land will be below relative sea level, and hundreds of millions of people will be at risk because of the land sinking.
Land subsidence can cause serious damage to the city's infrastructure in the first place, and the structure of buildings, bridges, roads, and pipelines can all crack or deform due to land subsidence, leading to safety hazards and increased maintenance costs.
Second, land subsidence can also cause water levels in rivers and oceans to rise and flood cities, hindering the normal operation of drainage systems and increasing the risk of flooding.
Causes of land subsidence
So why is this happening?
Land subsidence, which is what we call land subsidence.
This phenomenon itself exists in nature, such as natural factors such as crustal movements, earthquakes, floods, and weathering of underground rocks, which can cause changes in the stratigraphic structure and cause the ground to subside.
Human factors can also lead to a reduction in ground height, such as the overexploitation of underground resources and the huge weight of the subsoil brought by the built environment, which are the main causes of land subsidence.
Cases of land subsidence
The city with the most severe land subsidence on the mainland is Tianjin, with a rate of up to 52 mm per year.
In May 2023, due to land subsidence, there are obvious lower limits and cracks in the ground in a community in Tianjin, and even some houses are skewed. The land subsidence incident led to the emergency evacuation of nearly 3,000 people and had to evacuate to a safe area.
There was also a subsidence accident in Futian District, Shenzhen in March 2013, when a large pit with a diameter of 5 meters and a depth of about four floors suddenly appeared on the road.
It's terrible, isn't it, but the problem of land subsidence on the mainland is not very serious compared to other countries and regions in the world.
For example, in the Houston area of the United States, the land subsidence area has reached 8,000 square kilometers in the past century, and the cumulative subsidence in some areas has even exceeded 3.5 meters.
Jakarta, the capital of Indonesia, chose to move its capital due to an average annual subsidence rate of 17 centimeters.
Land subsidence and sea level rise
It is worth noting that the problem of land subsidence and sea level rise in many coastal cities often occur at the same time.
Due to global warming, melting polar glaciers and other problems, the global sea level has risen by 10-20 centimeters since the 20th century, and we cannot control the trend of sea level rise in the short term.
Response
Faced with such a situation, are we helpless?
At present, the world's measures for land subsidence and sea level rise are still dominated by groundwater resource management and coastal dam construction.
For example, in Osaka and Tokyo in the 70s of the last century, the pumping of groundwater was stopped in order to slow the rate of land subsidence, and now the phenomenon of urban subsidence has been greatly reduced.
Steep walled seawall for coastal protection works
On the mainland, Shanghai manages groundwater resources and builds coastal dikes. On the one hand, the groundwater management plan should be strictly implemented to achieve a balance between groundwater extraction and irrigation and prevent land subsidence. On the other hand, coastal dikes are being actively constructed to prevent the risk of flooding caused by rising sea levels.
Resources:
Land subsidence – Chinese Academy of Sciences
By 2040, 8% of the Earth's surface could subside
Sea levels along China's coast are 72 millimetres above average, still at the highest level since records began
"Nearly half of China's big cities are sinking"? Listen to what the author of the paper has to say - intellectuals